Genetic Variation Among Cultivated Selections of Mamey Sapote (Pouteria Spp

Proc. Fla. State Hort. Soc. 117:195-200. 2004. GENETIC VARIATION AMONG CULTIVATED SELECTIONS OF MAMEY SAPOTE (POUTERIA SPP. [SAPOTACEAE]) SUSAN CARRARA1 ideas about the differentiation between the three closely re- Florida International University lated species which produce the fruit commonly called “ma- Department of Biological Sciences mey sapote” have the potential to enlarge the range of traits 11200 SW 8th Street that should be represented in such a collection. Miami, FL 33158 This paper aims to facilitate mamey sapote germplasm collection expansion and management by identifying geograph- RICHARD CAMPBELL ic areas of high genetic diversity for future collection. This is Fairchild Tropical Botanic Garden accomplished by analyzing the genetic diversity of selections 11935 Old Cutler Road held by FTBG and the University of Florida’s Tropical Re- Miami, FL 33156 search and Education Center (TREC) using the Amplified Fragment Length Polymorphism (AFLP) technique. RAYMOND SCHNELL The mamey sapote selections in this study can be grouped United States Department of Agriculture-Agriculture Research Service into three main categories based on the region in which they 13601 Old Cutler Road were collected: Cuba, the Caribbean coast of Central America Miami, FL 33158 (specifically the Yucatán Peninsula, the Petén of Guatemala, and Belize), and the Pacific coast of Central America (Guate- mala, El Salvador, Nicaragua, and Costa Rica at elevations Additional index words. Mamey sapote, Pouteria spp., genetic from sea level to 1000 m) (Fig. 1). Genetic diversity of selec- diversity, AFLP tions from the Yucatán peninsula were hypothesized to be low due to their morphological similarity and to the land clearing Abstract. Mamey sapote (Pouteria spp., Sapotaceae) is a tree that occurred there during the Spanish conquest only 500 fruit of economic and cultural importance in South Florida, Central America, Mexico, and the Caribbean. This study is years ago (Landa 1978). among the first to analyze genetic variability among cultivated Concurrently, selections from the Pacific coast popula- selections of mamey sapote. The Amplified Fragment Length tion were hypothesized to have greater variation because Polymorphism (AFLP) technique was used to estimate levels there are three species present in the region whose fruit is of genetic diversity in the germplasm collections of Fairchild considered mamey sapote. Pouteria sapota is currently cultivat- Tropical Botanic Garden and University of Florida. Although ed throughout Central America and the Caribbean in a range the collections overall represent a low level of genetic diversi- of soil types at altitudes up to 1,200 m. Pouteria viridis shares ty, higher levels of genetic diversity were found among selec- the same geographical range as P. sapota, but tends to grow at tions from Central America. This indicates future plant a higher altitude (1000-1500 m). Pouteria fossicola is distribut- collection in that region could capture greater genetic diversi- ed further south than P. viridis and P. sapota with a range ex- ty. This information can be applied to the management and expansion of the germplasm collections by identifying duplicate tending from Nicaragua through Costa Rica to Panama selections, mislabeled plants, and locating geographical areas between 0 and 800 m above sea level (Pennington 1990). for future collection. Knowledge of, and access to, the full range of a crop’s genetic resources is vitally important to the continuing develop- ment of agriculture. Genetic diversity, the total number of different alleles present in a species, is an important component of a plant’s genetic resources. The distribution and scale of a crop’s genetic diversity must be understood before effec- tive germplasm collection can be undertaken. Comprehen- sive genetic information allows curators of living collections to optimize the genetic diversity in their collections, plan for efficient collection enlargement, and ultimately furnish a wid- er selection of plants to growers. Mamey sapote is a well known crop in South Florida, and has been described by Balerdi et al. (1996) and Léon (2000). Fairchild Tropical Botanic Garden (FTBG) holds one of the most representative and genetically diverse collections in the USA. Yet, a greater range of morphological traits can be observed in mamey sapote’s native or cultivated range than exist in the FTBG germplasm collection. In addition, changing Fig. 1. Map indicating the Pacific and Caribbean regions from which mamey sapote selections in the germplasm collections of Fairchild Tropical Bo- 1Corresponding author. Present address: P.O. Box 16581, Asheville, NC tanic Garden (FTBG) and the University of Florida’s Tropical Research and 28816. Education Center (TREC) were collected. Proc. Fla. State Hort. Soc. 117: 2004. 195 Fig. 2. UPGMA dendrogram of cultivated selections of mamey sapote in Fairchild Tropical Botanic Garden (FTBG) and the University of Florida’s Trop- ical Research and Education Center (TREC) germplasm collections in South Florida, USA. 196 Proc. Fla. State Hort. Soc. 117: 2004. Table 1. Mamey sapote sample material used in AFLP analysis of genetic Table 2. Analysis of Molecular Variance (AMOVA) for cultivated selections diversity present in the Fairchild Tropical Botanic Garden (FTBG) and of mamey sapote in Fairchild Tropical Botanic Garden (FTBG) and the the University of Florida’s Tropical Research and Education Center University of Florida’s Tropical Research and Education Center (TREC) (TREC) germplasm collections in South Florida, USA. germplasm collections in South Florida, USA. Population Group FTBG TREC Total Variance Source of variation df component Percentage Caribbean 13 1 14 Paciﬁc 10 3 13 Caribbean versus Paciﬁc regions Cuba 2 2 4 Between region 1 1.244 13% Florida 2 0 2 Within regions 27 8.216 87% Cuba or Florida 2 0 2 Control: same individuals distributed randomly into regions Other 2 0 2 Between regions 1 0.167 2% Unknown 0 6 6 Within regions 27 8.773 98% Total 31 12 43 Principal component analysis (PCA) supported the UPG- Materials and Methods MA-based cluster analysis. The first three axes summarized 20.6, 7.5 and 6.3% of the data set’s variability, respectively. A A total of 41 unique mamey sapote selections were analyzed, scatterplot of the first three principal components shows a including 29 individual selections from FTBG and 12 from tight cluster including the majority of the study selections, TREC (Table 1). Appendix 1 specifies collection location and with only the more diverse selections separating out (Fig. 3). replicate information for all selections included in this study. By removing outliers, the distribution can be seen more clear- Laboratory procedures were carried out in the USDA-ARS- ly (Fig. 4). SHRS Plant Sciences Laboratory using the ethanol-precipita- AMOVA results indicate 13% of the variance was attribut- tion based Epicentre MasterPure™ Plant Leaf DNA Purifica- able to genetic variation between the regions. This is higher tion Kit (Epicentre, Madison, Wis.). AFLP markers were than the between-region variance of control groups randomly generated using Applied Biosystem’s AFLP™ Ligation/Prese- assigned to populations (Table 2). Unfortunately, F statistics lective Amplification Module (Applied Biosystems, 2000). The are not relevant for use with AFLP data. protocol was modified by reducing reaction volumes by one Selection ‘2002-165 A’, which originated from a seed col- half to reduce costs and repeated twice for each selection. The lected in a fruit market in northern Costa Rica, is one of the resulting fragments were separated by capillary electrophore- more distinct selections. It was collected because the fruit had sis and fragment sizes were analyzed with Genotyper version morphological characteristics intermediate between P. sapota 3.7 (Applied Biosystems, Foster City, Calif.). and P. fossicola: a green skin with brown scruff on the nose. From the multitude of fragments produced, AFLP mark- Added to the morphological ambiguity between the two spe- ers were selected based on their consistency over two AFLP replicates of each sample. Fragment sizes identified by Geno- typer were manually verified. Mismatches between replicates were accepted as missing data, for a total of 1.4% missing data over a total of 104 markers. Pairwise similarity between samples was estimated using Nei and Li’s (1979) similarity coefficient, also known as the Dice coefficient, using NTSYS (Exeter Software, Setauket, N.Y.). Dendrograms were produced using the unweighted pair group method of analysis (UPGMA) (Sneath and Sokal, 1973). Confidence levels were placed on the dendrograms using 2000 bootstrap replications with the program WinBoot (Yap and Nelson, 1996). Finally, principle component analysis (PCA) performed by SPSS (SPSS, Inc., Chicago, Ill.) was used as another visualization of the data. Analysis of Molecular Variance (AMOVA) was used to assess differentiation between the Pacific and Caribbean populations (Excoffier et al., 1992). Results and Discussion Some grouping of the selections according to their collection location was observed in the UPGMA dendrogram but was not supported by the bootstrapping procedure, perhaps due to the high overall genetic similarity of the samples. How- ever, several trends can be noted. The majority of selections collected from the Yucatán and Cuba showed a high level of similarity. In addition, the selections collected in the Pacific Fig. 3. Principal component analysis of mamey

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